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BigC
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Reged: 09/29/10

Loc: SE Indiana
Re: Use of vintage eyepiece sun filters... Why not? new [Re: DAVIDG]
      #4614835 - 06/01/11 12:22 PM

That is really neat.So there is a good and proper use for uncoated mirrors.
One little note about safety: although the reflectivity of 1/4 of 1% sounds very safe,everyone should remember the scope is gathering considerably more light than the naked eye.So if the scope gathers 400 times as much as the naked eye ,then looking into the scope without the Herschel wedge would be like staring directly at the unmagnified sun.Bigger aperature scopes could be dangerous.
Wonder if one of the common cheap 76 Newts could have its mirrors stripped of coating and then be safe for solar viewing?


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Joe Cepleur
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Reged: 03/18/10

Loc: Dark North Woods
Re: Use of vintage eyepiece sun filters... Why not? new [Re: DAVIDG]
      #4614888 - 06/01/11 12:47 PM

Quote:

Eye damage is serious stuff... I have had a filter crack on me while I was observing the Sun and looking into the eyepiece when was I kid. Since then I have had my eye examined many times and told the Doctors what had happened and they could find nothing wrong with my eye.

(O)ver years I have read that when these filters crack one is going to suffer instant blindness. While this is very serious, I would like to know if anyone has FIRST hand knowledge of eye damage caused by one of these filters cracking...

(W)hy I built a telescope designed for white-light solar obsevering, with many built in safety features. If any part fails, it fails safe and no image can be formed at the eyepiece.




Glad to hear you are okay after the filter cracked. Perhaps the outcome would have been less fortunate had it shattered?

I have to agree, I have no first-hand knowledge of instant blindness occurring. It may be an urban myth, yet seems like a realistic possibility, one easily prevented by carefully securing an aperture filter in place; or, better yet, by building or buying a dedicated, fail-safe solar telescope. I vote that we continue to teach not to use these filters. If an errant telescope can burn a deck, there is no reason to risk damaging anyone's eyes.


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roscoe
curmudgeon
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Loc: NW Mass, inches from VT
Re: Use of vintage eyepiece sun filters... Why not? new [Re: BigC]
      #4614894 - 06/01/11 12:48 PM

Well...... I have a cheap .965 EP drifting around here somewhere that has a plastic field stop with an arc-shaped hole melted out of it........ no news of the former owner's eyeball, but glad it wasn't me!
Russ


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Jon Marinello
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Reged: 09/21/10

Loc: Santa Barbara, CA
Re: Use of vintage eyepiece sun filters... Why not? new [Re: wfj]
      #4615123 - 06/01/11 02:58 PM

I don't have a digital thermometer.

The tests I want to run are:

1. Star Diagonal Test - Solar filter mounted on a star diagonal

  • 60mm
  • 80mm
  • 90mm
  • 102mm

2. Eyepiece Test - Solar filter mounted on eyepiece

  • 60mm
  • 80mm
  • 90mm
  • 102mm - The results from this test are already known.


Let me start with these tests and we can add others after we have the results. I may not have enough filters to do all the tests. If anyone has any spares they can send me that would be appreciated.

I want to run the star diagonal tests first as these tests are less likely to break the filters I have. The problem is that I can't find a .965 star diagonal that has threads in the inside of the nose piece. I need to dig out the Sears scopes and check one of them...

So I'm blocked at the moment. Clouds just rolled in too!

jon


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wfj
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4615181 - 06/01/11 03:38 PM

It would not surprise me if you had a steady supply of these filters, that if you averaged the "accumulated exposure time" at prime focus to the sun ... they would all break around the same time (plus or minus a small scatter).

You'd end up with a Gaussian distribution, and this would prove that the issue is accumulated thermal stress/strain leading to a fracture along a weakest member.

Thus all these things ever were ... a limited lifetime component with a terrible failure mode.

What's even worse was that the cost trade-off of a small piece of welders glass verses a few square inches of aluminized mylar is tiny. Probably just happened because of the cost of the vacuum equipment for doing the coatings.


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actionhac
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: wfj]
      #4615318 - 06/01/11 05:18 PM

This is probably a silly question but will the SUN filter let enough light through to project an image on the solar projection screen?

Robert

Edited by actionhac (06/01/11 09:40 PM)


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Jon Marinello
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Loc: Santa Barbara, CA
Re: Use of vintage eyepiece sun filters... Why not? new [Re: actionhac]
      #4615319 - 06/01/11 05:20 PM

I'm only testing for the filter cracking nothing more. I won't look through it or use a camera.

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DAVIDG
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4615478 - 06/01/11 07:00 PM

Jon,
It might be possible to unscrew the barrel on the star diagonal and replace it with one from an eyepiece, that is thread for filters.
Also please make a note of how tight the filter is in the cell. It should rattle slightly when you shake it. If not I would loosen it, then run your tests and then repeat the tests with the filter tight in the cell.
It's been stated that these filters might shatter. Does anyone have first hand knowledge that a filter shattered ? I have seen them crack but not shatter. It's important to seperate the facts from the fiction and understand under what conditions these filters fail and how they fail.
It has been posted that these filters fail when used with telescopes that have apertures larger then 60mm. If the filter was designed for use on a 60mm telescope and failed when used with one larger, is that the fault of the filter or the user of the telescope ?

- Dave


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Joe Cepleur
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Reged: 03/18/10

Loc: Dark North Woods
Re: Use of vintage eyepiece sun filters... Why not? new [Re: DAVIDG]
      #4615540 - 06/01/11 07:40 PM

Quote:

If the filter was designed for use on a 60mm telescope and failed when used with one larger, is that the fault of the filter or the user of the telescope ?




It's customary but unfair to blame the user. The filter fits any scope with a 0.965" focuser. Realistically, what's likely to happen? Nothing stops it from being used in a scope of larger aperture. Ever notice the pump for diesel fuel will not fit the fill on gasoline powered car? That's good design, and the engineer's responsibility. Good engineering solves problems and protects people from unwitting harm. It's no secret that telescopes were often given to children, or used by adult beginners who did not read manuals

Quote:

if you averaged the "accumulated exposure time" at prime focus to the sun ... they would all break around the same time (plus or minus a small scatter)




Strictly, exposure time per unit area of objective (assuming consistent, bright sunlight). The point is the same. One filter is likely as robust (or imperfect) as the next. Whether or not blindness is a realistic risk, pain surely is, and one never knows when a particular filter will fail. 

It may sound morbid, but the army has data on how quickly a given intensity of light will blind an enemy hit with a laser weapon. A scope isn't a laser, but it intensifies light. Anyone know the facts, or care to research them?


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jsiska
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: BigC]
      #4615715 - 06/01/11 10:04 PM

Quote:

The little Sun filter was designed for use with a 60mm objective (or smaller) and you overloaded it with the light from a 100mm objective!Seriously ,it was subjected to 2/3rds more heat ;there really is a lot of energy in sunlight.



In my 1962 Tasco catalog, in addition to several 60mm refractors, the SUN filters also came with the Tasco 10TE Solarama 600 refractor which has a 76.2mm objective lens, and the 11TEA Lunagrosso which is a 4½” Newtonian.


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BarabinoSr
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Reged: 11/17/05

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Re: Use of vintage eyepiece sun filters... Why not? new [Re: jsiska]
      #4615796 - 06/01/11 10:55 PM

The TASCO 11TE 4.5" Lunagrosso has a lid that is a combination dust cover and light stop .It has a 2" removable cover that reduces the aperture to about 2" .G

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DAVIDG
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Reged: 12/02/04

Loc: Hockessin, De
Re: Use of vintage eyepiece sun filters... Why not? new [Re: BarabinoSr]
      #4615885 - 06/02/11 12:08 AM

I don't see how it is unfair to blame the user for using a filter on another telescope of larger aperture that is wasn't designed for and having it fail. Right now the data that has been posted show misuse as the mode of failure but there is very little data at all so you can't come to any type of conclusion. If the filters are provided with a 4" reflector or 80mm refractor and the instructions state to use a cap that reduces the aperture to 60mm with the filter and user fails to do this, this is failure of the user.
The original question was what is the reason why one shouldn't use these filters. We had failure when the filter was used on a telescope of larger aperture that the filter didn't come with. If the common mode of failure is misuse then we as a group need understand not to use them with a telescope they are not designed for and to also use them in correct manner on the telescope they were designed for. That is different then they are unsafe all the time. To make that determination we need data, not myths or second hand accounts.

- Dave


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Littlegreenman
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Reged: 05/09/05

Loc: Southern California
Re: Use of vintage eyepiece sun filters... Why not? new [Re: grendel]
      #4615917 - 06/02/11 12:32 AM

Quote:

(snip)....
when we run solar observing we always have a marshall, whose sole responsibility is to inspect each scope for safety, before and during the session. things that have been picked up vary from unfiltered finderscopes (which at best can result in burns to the forehead)....
Grendel




Slightly changing the subject, I once forgot to cover the finder on a C8 while solar viewing. This would have been a 6x30 finder. My forehead started to heat up. I moved around and saw bright glare coming from the finder, thankfully off to the side.

This is one of the few blessings of thinning hair. There wasn't any hair in the path to catch on fire!

(Almost blackened) Littlegreenman


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Joe Cepleur
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Reged: 03/18/10

Loc: Dark North Woods
Re: Use of vintage eyepiece sun filters... Why not? new [Re: Littlegreenman]
      #4615926 - 06/02/11 12:42 AM

Quote:

I don't see how it is unfair to blame the user for using a filter on another telescope of larger aperture that is wasn't designed for and having it fail. Right now the data that has been posted show misuse as the mode of failure but there is very little data at all so you can't come to any type of conclusion. If the filters are provided with a 4" reflector or 80mm refractor and the instructions state to use a cap that reduces the aperture to 60mm with the filter and user fails to do this, this is failure of the user.




It's unfair because the fault of bad engineering is then shifted to be blamed as the user's error.

If the engineering standard were that the filters would cover the entire objective, with so much absorption of light per square millimeter, then an oversized filter would in fact work fine, so long as the user found a sure means to secure it. Using an undersized might then properly be ascribed as the user's error: Duh; it didn't cover the entire objective. Fairly obviously, something intended to cover something else really needs to cover it.

A standard sized solar filter at the ocular fails this test. Any user could, not just by carelessness but by reasonable, expected human error, put the wrong filter in the wrong scope. The failure is thus the engineer's, for not designing a system that an ordinary human can use without error, every time, or risk hurting if not blinding his eyes.


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clintwhitman
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Reged: 01/01/07

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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4616050 - 06/02/11 04:09 AM

Hi All.
Without a Hershel Wedge in conjunction with a solar filer it is not "safe" to view the sun with any size refractor telescope. Other than that you can use a solar rejection mask that installs over the objective, but I find a Hershel wedge and a Zeiss ND filter to be the best setup for high magnification viewing of Sun spots with any size refractor. Also the optical flats that Unitron used in there solar wedges are very good and seem to work as well as Optima BC or Bader wedges.
As to taking readings of the heat generated at the focal plane of a telescope pointed at the sun. I can tell you the exact reading. Really Hot!!!
(aveman


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Rich (RLTYS)Moderator
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Re: Use of vintage eyepiece sun filters... Why not? [Re: actionhac]
      #4616125 - 06/02/11 06:26 AM

Quote:

This is probably a silly question but will the SUN filter let enough light through to project an image on the solar projection screen?

Robert




I wouldn't think so.

Rich (RLTYS)


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Joe Cepleur
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Reged: 03/18/10

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Re: Use of vintage eyepiece sun filters... Why not? [Re: Rich (RLTYS)]
      #4616201 - 06/02/11 07:54 AM

Quote:

how it is unfair to blame the user for using a filter on another telescope of larger aperture that is wasn't designed for and having it fail




Another thought: We're asking a fair question, "Has anyone heard, firsthand, of anyone being blinded when a filter failed?" Analogously, I can say that I, personally, have never once seen a solar filter of the design in question labeled, "Use only with 60mm aperture," or, "For 90mm aperture," or "For 100mm aperture or smaller." If they were designed for differently sized scopes, they would all have different darknesses of glass, yet would all look identically opaque to the eye selecting them, and so would need to be labeled. If they were intended only for 60mm scopes, none are so labeled, nor is there warning to use an accompanying aperture mask, except possibly in a manual that should be read, but may not be. The situation invites user error, a high stakes blame game when one is engineering a telescope for viewing the Sun. The solar filters of this design that I, personally, have seen all say only, "Sun," and some of them are molded in red plastic instead of black.

Red instead of black plastic is an imperfect example of engineering for safety. With the red color (grey to the colorblind), there is less chance that the user would insert the black moon filter by mistake prior to looking at the Sun and, at the very least, risking getting hurt. The trouble is, that black moon filter would still fit. A better example would be designating dedicated solar telescopes (such as exist, some of which are mentioned in this thread), and making special focusers for them, with square solar filters that simply could not fit into ordinary telescopes.This is not perfect, because the user might still find a means for attaching the wrong type of focuser to a supposedly solar scope. Still, at least with the right focuser when it was installed, that wonderful person everyone knows who has endless curiosity about the natural world, but little mechanical ability, could never be brought to harm accidentally via an error with a solar filter.

Trouble is, putting the solar filter at or near the focus of a conventional telescope exposes it to a far greater risk of breakage due to thermal issues, so it is inherently safer simply to move it to the safest place. Where's that? Before the objective. What light does not enter the scope can not hurt anyone's eyes. Granted, as Grendel discusses, it must be mounted securely, and the finder must be blocked; but, this is still a safer situation, one engineered to evade the user's ability to err.

People take all kinds of risks for all kinds of good reasons. No one is saying that no one else should never look at the Sun through a telescope. In gymnastics, the padding at the base of the apparatus (balance beam, uneven parallel bars, and the like) must extend past where the user is likely to land to also cover the steel feet. Why bother? Isn't it user error when the gymnast falls in the wrong place? What about steel toed shoes in the workplace. Isn't it user error when the employee drops something, or steps where told not to? Why waste the money covering the drive belts in heavy machinery? Isn't it user error when clothing gets caught, pulling the operator into the belt? Why should the petroleum industry make certain that the pump for diesel fuel won't fit in your gasoline powered car? Isn't the user responsible for selecting the correct hose?

In Maine recently, a vendor's kerosene tank was accidentally filled with gasoline. This could have killed anyone who poured the fuel into a kerosene powered heater and lit it. Why the concern, with all the radio stations, newspapers, and Web sites spreading the news? Isn't it user error if someone smells gasoline instead of kerosene, and lights it anyway? What about people with no sense of smell? Aren't they responsible to always have someone else smell their fuel? In this instance, the error was caught early, so no one got hurt. It would not have occurred at all if, as with the diesel-versus-gasoline hoses for cars, the fill on the kerosene tank were engineered to be unique, so the vendor could not have made the mistake that put others at risk.

This forum is unusual in at once being a hobbyist's abode and, in the marketplace of ideas, a respected, authoritative source of information. If we say, "Use the filters," more people will; and, if we say, "Do not!" more people will not. If Jon's tests show that his remaining five or so filters do not fail under whatever conditions, that would be interesting to know, yet would not prove that no filter would ever fail out in the wild world of well intended, but possibly naive users. Given the flawed design of these old-style solar filters sitting near the focus, let alone the unknowns in the current quality of the materials in any particular filter as they all age well past thirty, forty, and even fifty years, we have a responsibility to tell the world that, as much as we love classic telescopes, we want astronomers to consign this badly engineered design to the history books and use modern filters when viewing the Sun. Equal caution and better solar filters can only result in fewer injuries, whether mild or severe.


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EJN
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Reged: 11/01/05

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Re: Use of vintage eyepiece sun filters... Why not? [Re: DAVIDG]
      #4616623 - 06/02/11 12:49 PM

My first telescope was a Tasco 66TE 50mm f/12 which came
with a sun filter, that was in 1967. Not knowing any better**,
I used it for solar observation for years, including the
eclipse of March 7 1970 which was partial from my location.
I remember it would get quite warm after prolonged use. I
also remember that the optical quality was excellent, I
could see solar granulation when seeing was good. Later,
when I made a 6" Newtonian, I tried it in that and it cracked.
Not shattered, a single hairline crack. I wasn't looking
in the eyepiece when it happened, I heard a "snap" and took
it out & saw the crack.





** I was 10 then and there were no dire warnings on the internet
about eyepiece solar filters, most likely because the internet
did not exist then.


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Jon Marinello
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Loc: Santa Barbara, CA
Re: Use of vintage eyepiece sun filters... Why not? [Re: Jon Marinello]
      #4616708 - 06/02/11 01:38 PM Attachment (64 downloads)

I just started test (1, 60mm) at 10:25 PST. I was able to use an eyepiece barrel threaded into the star diagonal which allowed me to then thread the sun filter into the diagonal. That was a good suggestion. I will leave it pointed at the sun for a maximum of 2 hours. I have to run to a doctor's appointment at 11:00. I will check it before I leave and after I get back. This is the test that is most likely to succeed (i.e., not crack the filter of all the tests). Will report back later today on the result.

BTW - I have included a shot of the 60mm on my Atlas EQ-G so you can see what I am using for tracking for each of the tests.


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Jon Marinello
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Reged: 09/21/10

Loc: Santa Barbara, CA
Re: Use of vintage eyepiece sun filters... Why not? [Re: Jon Marinello]
      #4616714 - 06/02/11 01:40 PM Attachment (64 downloads)

The OTA for this test is a Sears Discoverer No. 4 6305-A D=60mm F=900mm. Here is a close up.

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